Section Information

Educational

Copyright

IPS welcomes the use of its material by others. Please read the
terms of use.

Commencement of Solar Cycle 24

The appearance of a reverse polarity
sunspot at the
relatively high latitude of 30 degrees north on 4 January, 2008 has been
accepted by space scientists as the first sign of solar cycle 24. At the time
this indicated solar minimum was not too far off and in fact occurred in
December 2008.

The Solar Cycle

The Sun exhibits a periodic cycle of activity over approximately 11 years
called the solar cycle. The number of sunspots is used to gauge the extent of
this activity and the
sunspot number
is a count of sunspots and sunspot groups on the visible disc of the Sun.

A solar cycle begins at solar minimum with little solar
activity and few sunspots on the Sun. As the cycle evolves increasing
numbers of sunspots appear and events such as flares and coronal mass
ejections increase in number. The peak in the sunspot number is called
solar maximum. Solar activity then gradually declines
returning to solar minimum and the end of the cycle. The plot of
sunspot number vs time shows the progression of the
cycle.

Sunspots and the Butterfly Diagram

A few months prior to solar minimum there are likely to be sunspots
associated with both the new and old cycles. Those associated with the old
cycle appear near the solar equator while new cycle sunspots emerge at higher
latitudes (30 to 50 degrees). Around solar minimum the old cycle sunspots
eventually disappear leaving only the new cycle spots. As the new cycle
passes through solar maximum towards the next solar minimum and its end,
sunspots emerge closer to the equator. A plot of this progression in sunspot
location over the solar cycle from higher to lower latitudes is called the
butterfly diagram for obvious reasons.

Satellite Eclipse Season

For about 21 days either side of the March and September equinoxes,
satellites in geo-stationary orbits pass through the Earth's shadow. Read
more on
satellite eclipses.

Geo-stationary satellite transmissions to Earth are subject to interference
from the Sun around the equinoxes when the Sun, satellite and Earth receivers
line up. An Earth receiver captures not only the satellite signal but also
unwanted signal from the Sun (noise). The noise strength can overwhelm the
satellite signal strength. Learn
more and see when interference is likely with
the
IPS Sun-Satellite Interference Prediction Tool.